1. Field of the Invention
The present invention relates to a negative image recording medium capable of being recorded by infrared laser, and more particularly, it relates to a negative image recording material in which an image part of a recording layer has high strength and which is capable of forming a lithographic printing plate excellent in printing durability.
2. Description of the Related Art
Laser technologies have been greatly developed in recent years, and particularly, a solid laser and a semiconductor laser which have an emission region over a near infrared ray region to an infrared ray region have become powerful and smaller in size. Therefore, these laser technologies are useful as an exposure light source for producing plates directly from digital data from, for example, computers.
A material for a negative lithographic printing plate for an infrared laser, to which an infrared laser having an emission region over a near infrared ray region to an infrared ray region is applied as an exposure light source, has a photosensitive layer containing an infrared ray absorbent, a polymerization initiator generating radicals by light or heat, and a polymerizable compound.
In general, the negative image recording material utilizes a recording method in which a polymerization reaction is caused by radicals which are initiator and are generated due to light or heat. The recording layer is thereby hardened in the exposed part to form an image part. The negative image recording material has low image forming property in comparison to a positive type causing solubilization of a recording layer due to energy from infrared laser irradiation, and a heat treatment is generally carried out before a developing step in order to form a firm image part by accelerating the hardening reaction through polymerization.
As such a printing plate that has a recording layer polymerizable by light or heat, techniques using a photopolymerizable composition or a heat polymerizable composition in a photosensitive layer have been known as described in JP-A-8-108621 and JP-A-9-34110. While the photosensitive layers are excellent in high sensitive image forming property, the adhesion at an interface between the photosensitive layer and a support is low in the case where a substrate that has been subjected to a hydrophilic treatment is used, whereby such a problem occurs that the printing durability is poor.
Furthermore, while the use of an infrared laser of high output is considered to increase the sensitivity, it causes such a problem that ablation of the photosensitive layer occurs at the time of scanning by the laser to thereby contaminate the optical system.